I've succesfully recultured from achel and westmalle - they both use the same yeast, as does westvletern. ANd also achouffe, which like almost all good belgian beers (i.e. not leffe) is bottle conditioned with fresh yeast - usually the same strain as primary, it should say it on the label in French 'refermentation en boteille' for wallonian Achouffe or in flemish for the flemish beers.
You
can use them for primary but the general advice I've seen and read (e.g. in Brew Like a Monk) is to use the wyeast or white labs versions for primary as they are more reliable and these are often multiple-strains and the yeast in the bottle may have v. different characteristics from how it would act if pure. A good use for the captured yeast is to add it at bottling stage so it can do its thing as the beers develop - which is what I'm doing with my Orval style beer. Or blend the dregs together to make a mixed belgian culture (like wlp575 which is rochefort + chimay + acouffe mix!) and see what happens!
That's certainly the 'ideal' (see
http://www.mrmalty.com/yeast.htm fro strain guides and origins for wyeast and white labs) but it is expensive - if you took the yeast from more than one bottle and reculture you should do fine if it's built up sufficiently to make a good-sized starter for a reasonable-gravity wort (maybe a dubbel not a trippel) so can work fine. Good way can be to make a 'single' (lowish gravity beer) and then use the yeast cake from that to drop a trippel on to - what better way to make up a huge starter than with a beer!
The fermentation temps have a HUGE influence on character - you want it warm but not too hot or it can go all bubblegummy (I'd say mid 20s are best - good table in Brew Like a Monk)
I'm off there in the van after Easter - good to hear prices can still be so low!
